1. Field of the Invention
The present invention relates to a method for removing a crack in an electromechanical rotor in which a number of slots are provided in an axial direction in an outer peripheral surface of a rotor core portion, a coil and a plurality of wedges are respectively inserted in lower portions and upper portions in the slots, and the coil is fixed in the slots by the wedges, a method for preventing crack growth in the same, an electromechanical rotor and a rotary electrical machine.
2. Description of the Related Art
As an example of the conventional electromechanical rotor, the construction of a turbine generator rotor 300 will be described with reference to FIGS. 7 to 13.
FIG. 7 is a view schematically showing a section of a part of the conventional turbine generator rotor 300, and FIG. 8 is a view schematically showing a surface perpendicular to the axial direction of the turbine generator rotor 300 shown in FIG. 7 with a part of it as a section. FIG. 9 is a perspective view schematically showing the assembly state of a slot 303 and a wedge 305 in FIG. 8. FIG. 10 is a plane view showing a deformed rotor shaft 301. FIG. 11 is a perspective view showing the turbine generator rotor 300 having a crack in a rotor dovetail portion. FIGS. 12 and 13 are perspective views of the turbine generator rotor 300 for explaining the conventional method for removing a crack occurring to the rotor dovetail portion.
As shown in FIGS. 7 to 9, the turbine generator rotor 300 includes a rotor core portion 302 formed integrally with the rotor shaft 301, and a number of slots 303 are provided in the axial direction in the rotor core portion 302. A coil 304 is inserted into the lower portions in each of the slots, and a plurality of wedges 305 are placed on the coil 304 via an insulating block 306. The wedges 305 are placed by being inserted in an insertion groove at an upper portion in the slot 303, and prevent the coil 304 from escaping from the inside of the slot 303 by a centrifugal force caused by rotation of the rotor shaft 301.
The wedge 305 may be formed into each of various shapes, but is generally formed into a dovetail shape as shown in FIG. 9, and is sometimes formed into a shape such as a T-shape, a Christmas tree shape or the like. Since a plurality of wedges 305 are inserted into the slot 303, a contact end portion 308 where the end surfaces of the wedges 305 adjacent to each other is formed on a contact surface 307 of the wedge 305 and the slot 303. On the contact end portion 308, not only the contact pressure by the centrifugal force concentrates, but also a relative slip ±δ occurs between the slot 303 (rotor core portion 302) and the wedge 305 when the rotor core portion 302 is bent with a curvature r by the tare weight or bending vibration and rotates as shown in FIG. 10. Therefore, large tensile and compression stress concentrates on the contact end portion 308 at the side of the rotor core portion 302 in the slipping direction. Therefore, a fretting damage occurs to this portion and a crack due to fatigue sometimes occurs.
When the radius of the rotor core portion 302 is set as ro, and the length of the wedge 305 is set as L as shown in FIG. 10, the rotor core portion 302 extends and contracts by δ shown in the following formula (1) at the position corresponding to the wedge end portion when it reaches the upper point A and the lower point B, but the wedge 305 is divided in the longitudinal direction, and therefore, does not extend or contract. Accordingly, a relative slip 2δ is caused at the contact end portion 308 of the wedge 305 and the rotor core portion 302 at each rotation of the rotor shaft 301.δ=ro·L/2r  formula (1)
As described above, the contact pressure concentrates on the contact end portion 308, and when the contact surface at high contact pressure is accompanied with slip, a crack 309 as shown in FIG. 11 sometimes occurs to the contact surface 307 at the side of the rotor core portion 302 due to a fretting damage.
Further, the crack 309 which occurs to the contact surface 307 at the side of the rotor core portion 302 is likely to grow due to bending stress occurring when the rotor core portion 302 performs bending rotation with the curvature r by the tare weight or bending vibration, thermal stress due to the temperature difference between the outside diameter side and the inside diameter side of the rotor core portion 302 at the time of operation of the turbine generator, residual stress of the material and the like. Therefore, for example, U.S. Pat. No. 6,849,972 discloses the art of removing the crack 309 which occurs to the contact surface 307 at the side of the rotor core portion 302 at the time of regular inspection or the like.
In the conventional crack removing method, the periphery of the crack occurring to the contact surface 307 of the rotor core portion 302 is notched and removed in accordance with the occurrence state, the size of the crack and the like, and a crack removed portion 310 is formed as shown in FIGS. 12 and 13.
Further, JP-B2 HEI 4-29304 (KOKOKU) discloses the art of providing a groove for relieving stress concentration on the contact end portion 308 at the side of the rotor core portion 302, and relieving concentration of the tensile and compression stress in the slipping direction on the contact end portion due to relative slip of the wedge 305 and the rotor core portion 302. Further, JP-B2 HEI 5-74304 (KOKOKU), JP-B2 HEI 7-40774 (KOKOKU) and JP-B2 HEI 7-44802 (KOKOKU) also disclose the art of reducing and preventing fretting fatigue of the contact surface 307 at the side of the rotor core portion 302.
The above described conventional art of removing the crack 309 occurring to the contact surface 307 at the side of the rotor core portion 302 requires a machining operation of a narrow portion inside the slot 303, and has the disadvantage of being unfavorable in workability. Further, the conventional art of relieving concentration of the tensile and compression stress in the slipping direction on the contact end portion due to relative slip of the wedge 305 and the rotor core portion 302, and the art of reducing and preventing the fretting fatigue of the contact surface 307 at the side of the rotor core portion 302 are the arts of preventing occurrence of a crack due to fretting fatigue, and are not the arts of removing a crack which occurs, or preventing crack growth.